1. Field of the Invention
The present invention relates to a semiconductor device, and a method for manufacturing the semiconductor device to reduce plasma charging damage generated during manufacturing of the semiconductor.
2. Background of the Related Art
A related art semiconductor device will be described with reference to FIG. 1. As shown in FIG. 1, when forming a twin well semiconductor device, a n-type well 4 is selectively formed at a required place on a p-type semiconductor substrate 2.
To form a triple well structure, in addition to the n-type well 4, a n-type deep well 5 is selectively formed, and a p-type well 3 is formed within the n-type deep well 5.
Consequently, in either the twin and triple well structures, a current path is formed by charged plasma 1 creating a current during the manufacturing process as follows (1) current path 6 formed by p-type well 3⇄p-type substrate 2⇄p-type well 3; or current path 7 formed by p-type well 3⇄p-type substrate 2⇄n-type well 4.
If any device including a gate oxide film, for example, a MOSFET device, is located in the current path, the gate oxide film sustains damage from the plasma 1 charge.
In general, when manufacturing a semiconductor device using plasma equipment, for example, an etching process for gate patterning, metal etching, interlayer dielectric (ILD) process, inter metal dielectric (IMD) process, and photoresist ashing, a voltage is applied to the gate oxide film during the manufacturing process.
Due to the inequality of the electric charge of the plasma 1, electric charges of differing amounts accumulate on the gate according to a position of a transistor on an wafer. The electric charges accumulated on the gates induce a voltage to the gate oxide film in a MOS capacitor.
Such a voltage causes a Fowler Nordheim (FN) tunnelling current flow through the gate oxide film, thereby, irreversibly damaging the gate oxide film.
The damage to a gate oxide film destroys or lowers the insulator characteristics of the gate oxide film. As a result, the transistor or MOSFET does not operate normally.
For example, if a negative charge density is high in a certain portion of the device while a positive charge density is high in another portion of the device, current paths (6) and (7) of FIG. 1 are formed, and a current flows.
In general, since each transistor is located close to other transistors on a chip, the difference between charge density accumulated on the gates is relatively small as compared to the difference between the gate charge density of transistors located in different chips.
Therefore, most plasma charge damage is not generated through the current path formed between the same chips or adjacent chips, but through the current path formed between the chips relatively distant from each other.
Even in the case of using a n-type semiconductor substrate, rather than a p-type semiconductor substrate, the same plasma charge damage occurs.
The related art semiconductor device and method for manufacturing the semiconductor device have the following problems.
Current paths are formed between wells located in a chip formation area. As a result, a degradation of gate oxide film may be generated by the plasma charge during the process of manufacturing the device. Such degradation of the gate oxide film destroys or lowers the characteristic of the gate oxide film as an insulator, preventing the transistor from operating normally, and reducing the reliability of the device.